1. Field of the Invention
The present invention relates to a signal transceiver, and more particularly, to a signal transceiver which provides good return loss when the signal transceiver operates in a power-off state.
2. Description of the Prior Art
Ethernet over Coax (EoC) is a transmission technology in which the Ethernet signals are transmitted over a coaxial cable. The objective of EoC is to connect home appliances or computing devices to the Internet by using the existing cable television infrastructure, wherein the signals transmitted on the cable for EoC should be compatible with the existing cable (or satellite TV) broadcast signals so that data for two different services (i.e. EoC and TV) can be simultaneously transmitted over the same coaxial cable. Among all methods proposed for EoC, the multimedia network standard developed by the multimedia over coax alliance (MoCA) is capable of providing high speed and high quality of service (QoS) functionalities, which are essential for glitch-free streaming media. According to the multimedia network standard, signals can be sent to each client through the existing coaxial cable, and the client only needs a signal transceiver to demodulate the signals transmitted over the cable to obtain the services.
Please refer to FIG. 1, which is a schematic diagram of a conventional signal transceiver 10. The signal transceiver 10 includes a connector 100, a band-pass filter (BPF) 102 and a front-end module 104. Usually, the signal transceiver 10 is implemented with a set-top box (STB). The connector 100 connects a coaxial cable for receiving signals including a MoCA signal, which is transmitted via the coaxial cable. The band-pass filter 102 is utilized for allowing signals within an operational frequency of the signal transceiver 10 to pass while filtering out unwanted signals outside the operational frequency. For example, the range of the frequency band of the MoCA signal provided by the U.S. satellite TV service provider DIRECTV™ is from 475 MHz to 625 MHz. If only the MoCA signal needs to be passed, the frequency range of the band-pass filter 102 should be designed to pass signals from 475 MHz to 625 MHz. The front-end module 104 is utilized for demodulating the signals which have passed through the band-pass filter 102. In general, the front-end module 104, which is usually integrated into an integrated circuit (IC), includes circuits such as a transmitter-receiver, a power amplifier and an attenuator.
Please refer to FIG. 2A and FIG. 2B, which are schematic diagrams of the return loss at the point where a coaxial cable (not shown) connects to the connector 100 when the signal transceiver 10 operates in the power-on state and the power-off state, respectively. As can be seen from FIG. 2A and FIG. 2B, the minimum return loss of the signal transceiver 10 in the power-off state is nearly 7.6 dB, which is 3.4 dB lower than in the power-on state (nearly 11 dB) within the frequency band of 475-625 MHz. Therefore, the system may suffer from performance degradation due to low return loss in the power-off state.